Thank you for discussing the new feature here. This is how I understood adaptive and responsive images by now:

While responsive images are mainly used to respond to the viewport (scaling), adaptive images try to give a better answer to connection speeds.

The solution which is discussed here seems to be something in the middle. I mean - it is great to be able to deliver images as a respond to viewport, display width and density, but how will all the people feel who have the greatest new mobile phones but very bad connections to the internet?

Will mobile phones with bad connections ever learn to ask for smaller images or will we have to use one more script to block the big pics in these cases? It is not very easy to find a good answer to (retina) performance issues. Right?